The present invention relates to an oven for drying or curing articles and particularly relates to a reversible, convection air, cross flow drying or curing oven. More particularly, the present invention relates to a drying or curing oven providing for manual or automatic reversal of cross flow convection air currents within the oven at periodic intervals to obtain uniform drying or curing characteristics substantially throughout the entirety of the oven.
In batch type ovens, workpieces are frequently placed on carts and disposed in the work zone or heat chamber of the oven for drying or curing. Heated air is then supplied to the oven chamber through various ductwork and the workpieces are dried or cured over time. The flow pattern of the convection air current thus obtains a uniformity with time within the oven chamber. A uniform air flow pattern over a substantial period of time, however, creates temperature gradients within the oven chamber. For example, in certain ovens, the ductwork is arranged to flow heated air from one side of the oven to the opposite side or vertically between the top and bottom of the oven. The incoming air on the supply side is thus hotter than the outgoing air on the return side. This causes the workpieces adjacent the incoming supply of hot air to dry or cure at a rate faster than the workpieces located adjacent the relatively cooler, through heated, air near the return side of the oven. Thus, the drying or curing characteristics of the workpieces vary dependent upon their location within the oven because a different temperature is applied thereto at each location.
This variance in temperature within the oven chamber is particularly critical in drying or curing flat sheets, for example, capacitor components which may vary in size from 81/2 inches by 11 inches to 4 feet by 8 feet. Flat sheets will often warp, crack or otherwise distort when hot air at different temperatures is applied over the entirety of the surface of the sheets. Moreover, it will be appreciated from the foregoing that the optimum over residence time for proper drying or curing of workpieces in batch type ovens is not dependent on the workpiece which first dries or cures. Rather, if all the workpieces are to be dried or cured, the residency time for all workpieces within the oven is dependent on the workpiece which last dries or cures. Thus, economy of oven operation is sacrificed in those batch type ovens where temperature gradients exist if all workpieces are to be entirely dried or cured over the proper period of time. Also, economy of oven operation is affected by the temperature necessary to dry or cure the workpieces. For example, in batch type ovens, the temperature of the incoming air is usually higher than necessary in order that the workpieces closest to the return will be dried or cured at the designed temperature. Thus, because of the existence of temperature gradients in batch ovens, heated air must be supplied at non-optimum; e.g., higher, temperatures. The operation of the oven therefore requires substantially greater energy input than would be necessary if uniform temperatures could be maintained throughout the oven chamber. Accordingly, there has arisen a need for a new and improved drying or curing oven of the convection air current type which minimizes or eliminates the foregoing and other problems associated with prior convection air current drying or curing ovens and provides a heated air flow pattern affording substantially uniform heating of the workpieces over the duration of their time within the oven.